Lung diseases caused by bacterial or viral agents pose a serious problem for farmers and cattle ranchers. One example, porcine pleuropneumoniae in pigs which is caused by the bacterium Actinobacillus pleuropneumoniae, costs pork producers millions of dollars each year. The disease has a complex pathogenesis, and a secreted cytotoxin plays an important role in the production of acute lung lesions. Another example, bovine respiratory disease complex (shipping fever), is a severe fibrinous pneumonia that has had an economic impact on feedlot and stocker cattle. Shipping fever has a complex etiology, with the probable cause of the disease being a combination of environmental stress factors and viral and bacterial infection.
To protect animals from lung disease, it is essential to achieve a sufficiently high level of IgA antibodies in the lungs to prevent adherence of invading microorganisms to mucosal surfaces and neutralize potentially damaging virulence factors. Although attempts have been made to develop methods to deliver antigens to the lungs to stimulate antibody production, there are significant drawbacks to existing methods of immunization. Administration of vaccines by intramuscular or subcutaneous injection do not provide sufficiently high levels of IgA antibodies in lung fluids. Intratracheal or intranasal delivery of antigens by cannulation or aerosolization are labor-intensive and not practical for routine or large-scale application. In addition, the ciliated mucosa of the pulmonary tract functions in a manner that removes foreign antigens, which makes it difficult to deliver a reliable and immunologically effective amount of an antigen to the lungs by such methods.
The difficulties in administering antigens to the lungs has contributed to the present lack of efficacious vaccines for the prevention of bacterial and viral-induced infections of the lungs. Therefore, a need exists for an effective, simple method for vaccinating an animal against lung disease.